Field of the Invention
The present invention relates to a safety mechanism of a cylindrical battery.
Description of the Related Art
FIGS. 17 to 20 illustrate a structure of an alkaline battery 100 (cylindrical alkaline battery of type LR6). In these drawings, FIG. 17 is a longitudinal sectional view illustrating the alkaline battery 100 when a direction extending the cylindrical axis of the alkaline battery 100 is defined as a longitudinal direction, and FIG. 18 is an enlarged view illustrating an anode terminal plate and therearound of the alkaline battery 100 in FIG. 17.
As illustrated in FIG. 17, the alkaline battery 100 includes: a metal cathode can 11 in a bottomed cylindrical shape; a cathode mixture 21 in an annular shape, a bottomed cylindrical separator 22 provided in the inner side the cathode mixture 21, an anode mixture 23 (anode gel), containing zinc alloy, with which the inner side of the separator 22 is filled, an anode current collector 31 that inserted into the anode mixture 23, an anode terminal plate 32 having an appearance of a substantially dish-shape that is provided to an opening of the cathode can 11, a sealing gasket 35 provided below the anode terminal plate 32 when the opening of the cathode can 11 is placed upward, a washer 50 attached around the outer periphery of a peripheral side surface 32b of the anode terminal plate 32; and the like. Among the above, the cathode mixture 21, the separator 22, and the anode mixture 23 constitute power generation elements of the alkaline battery 100 in the presence of an alkaline electrolyte.
As illustrated in FIG. 18, a thin-walled portion 35b is formed in the sealing gasket 35. When the internal pressure of the alkaline battery 100 is increased for some reason, the thin-walled portion 35b is broken prior to other parts of the sealing gasket 35, so that the gas blowing out from such a broken part to a space 181 between the anode terminal plate 32 and the sealing gasket 35, is released through a vent hole 32c, provided in the peripheral side surface 32b of a dish-shaped portion in the anode terminal plate 32, to the outside of the space 181.
The washer 50 is provided for the purpose of restraining short circuit (preventing short circuit between the anode terminal plate 32 and the cathode can 11) and the like. FIGS. 19 and 20 illustrate a structure of a washer 50. FIG. 19 is a plan view illustrating the washer 50 when seen from the opening of the cathode can 11, and FIG. 20 is a perspective view illustrating the washer 50. As illustrated in these drawings, the washer 50 is in such a shape that a flange portion 50c is formed on the upper end surface of a flat hollow cylindrical washer boss portion 50a. 
Here, as illustrated in FIG. 18, the gas blowing out form the broken part of the thin-walled portion 35b passes from the vent hole 32c through a narrow gap between components to the outside, as indicated by arrows in the drawing. Therefore, when a large amount of gas is generated inside the battery for some reason, releasing of the gas may be too late, which may increase the pressure of the gas, to detach the washer 50.
As a technique for preventing such detachment of the washer 50, for example, Japanese Patent Application Laid-open Publication No. 2012-59616 describes that a notch portion is formed on a cylindrical side surface of a barrel portion of a washer, and a part of the pressure applied to the inside of the barrel portion of the washer is released, to prevent the washer itself from flying (being detached). Further, Unexamined Utility Model Application Publication No. 7-14555 describes that an insulating washer is formed such that the greater the force of the insulating washer being detached from an anode terminal becomes, the greater the contact resistance between the insulating washer and a rising portion of the anode terminal becomes.
As described above, from the safety point of view, the above washer 50 constituting the alkaline battery 100 needs to be structured in such a manner as not to be detached even if a large amount of gas is generated inside a battery for some reason. However, from the view point of improvement of productivity, the above washer 50 needs to be structured considering the ease of forming and the certainty of forming (improvement in yield).
The present disclosure has been made from such view points, and an object thereof is to provide a cylindrical battery excellent in safety and productivity.